Indirectly heated cathodes with filament support for use in electric discharge tubes



Jan. 30, 1968 P. M. DE BAKKER' .INDIRECTLY HEATED (JATHODES WITH FIIJAMENT SUPPORT FOR USE IN ELECTRIC DISCHARGE TUBES Filed Nov. 18, 1965 INVENTOR. PETRUS M.DE BAKKER AGENE United States Patent 3,366,827 INDIRECTLY HEATED CATHODES WITH FILA- MENT SUPPORT FOR USE IN ELECTRIC DIS- CHARGE TUBES Petrus Modestus De Bakker, Emmasingel, Eindhoven, Netherlands, assignor to North American Philips, Company, Inc., New York, N.Y., a corporation of Delaware Filed Nov. 18, 1965, Ser. No. 508,464 Claims priority, application Netherlands, Dec. 10, 1964, 6414,340 2' Claims. (Cl. 313-270) ABSTRACT OF THE DISCLOSURE An indirectly-heated cathode for an electric discharge tube employing a folded filament supported at one end by an inwardly projecting extension of the cathode sleeve.

The invention relates to an indirectly heated cathode for use in an electric discharge tube, said cathode consisting of a tubular sleeve as a support for the emissive layer in which a heating body formed by one or more :parts coated, if required, with insulating material, is arranged.

In order to facilitate the connection of the ends of the filament wire of a heating body of an indirectly heated cathode with the current supply conductors, it is important that these ends should protrude always over the same distance from the cathode sleeve. Particularly in the case of automatic mounting this is essential.

In order to have a short heatingmp time of a cathode, use is made in many cases of filament wire which is :folded once of several times and which may, if required, be coated with insulating material and is slipped into the tubular cathode sleeve without the remaining space in the sleeve being filled out further.

Since the folded filament wire is loosely included in the cathode sleeve, it can readily shift in place during the mounting operation, so that the lengths of the protruding ends of the filament wire may be different. Since, moreover, in -a vertical cathode the whole weight of the filament wire bears on the ends connected with the current supply conductors, the filament wire may bend outwardly near said ends over the portion protruding from the cathode sleeve. The tips of the V- or hairpin-shaped parts of the heating body then sink down gradually more deeply in the cathode sleeve. This results in a non-uniform heat distribution along the cathode sleeve, while various cathodes of the same type may exhibit great differences in temperature. Moreover, the insulating material may scale off the curved ends so that short-circuit may be produced, when these curved ends come into contact with each other or with other conductors.

Said disadvantages can be completely avoided, if in accordance with the invention at least one re-entrance extension is provided in the cathode sleeve near one of the ends, said extension being located in the tip between the limbs of one or more folded parts of the heating body.

If the cathode is arranged vertically, each folded part of the heating body is thus suspended so to say by its tip on the inwardly projecting extension of the cathode sleeve. The position of the tip is thus fixed and hence also that of the ends of the filament wire. Particularly for automatic mounting this is very advantageous, since the places for fastening the said ends to the current supply conductors are fixed.

It is known to fix a filament wire in a cathode sleeve near one end by means of a droplet of insulating material introduced into the sleeve, but this method is circuitous, while it cannot be checked satisfactorily whether the heating body has been fastened correctly. Moreover,

difficulties may arise from the expansion of the metal parts of the cathode and the heating body.

The invention will be described more fully with reference to the drawing, in which FIGS. 1, 2, 3, 4, 5 and 6 show various embodiments of cathodes according to the invention.

Referring to the figures, reference numeral 1 designates the tubular sleeve on which the emissive layer (not shown) is provided. Reference numeral 2 denotes the heating body consisting of parts folded once or several times. Each V- or hainpin-shaped part has a tip 4, which is suspended on a part projecting inwardly in the cathode sleeve 1. FIG. 1 shows the extension 3 parallel to the longitudinal axis of the cathode sleeve. In order to reduce the risk of scaling off of the insulating layer from the tip 4 of the heating body 1 on the narrow edge of the extension 3, this extension may be arranged at right angles to the axis of the cathode, which is indicated by 6 in FIGS. 2, 5 and 6. FIG. 3 shows two re-entrant parts 7 opposite each other in the wall of the cathode sleeve so that the heating body 2 can be suspended on the tips of the re-entrant parts 7.

When the cathode sleeves has a .greater width, a ceramic tube 8 may be clamped between the re-entrant parts 7, as is shown in FIG. 4, the tip 4 of the heating body 2 being suspended on said tube. In this case the filament wire may be uncovered and the cathode sleeve may be coated internally with an insulating layer 9.

If the heating body 2 comprises a plurality of folded parts, an extension 6 may be provided for each part, which is shown in FIG. 5. The extensions 6 may, if desired, be shaped in the .form of the extension 3 (if FIG. 1.

As a iurther alternative, the two folded parts of the heating body 2 may be suspended side by side on one extension 6, which is shown in FIG. 6.

The heating body with the limbs of each folded part one on eachside of the extensions 3, 6 or 7 is slipped from above into the cathode sleeve until the tip 4 bears on the extension. The ends 5 then protrude invariably over a given length from the lower end of the cathode sleeve, so that they can be automatically connected with current supply conductors, which have a defined position and place, for example by soldering, welding or clamping.

Although several embodiments are described above, the invention is not restrictive thereto. The cross section of the cathode sleeve may be rectangular, but it may have any other suitable shape.

What is claimed is:

1. An indirectly heated cathode :for use in an electric discharge tube, said cathode consisting of a tubular sleeve as a support for the emissive layer, in which a heating body consisting of folded parts, coated, if required, with insulating material is accommodated, in which near one of the ends of the cathode sleeve there is provided at least one inwardly projecting extension which is located at the tip between the limbs of one or more folded pants of the heating body.

2. A cathode as claimed in claim 1, in which the extensions are formed by re-entrant parts of the wall of the cathode sleeve.

References Cited UNITED STATES PATENTS 2,143,915 1/1939 Jobst 313340 2,155,237 4/1939 Perr-o'tt 313-337 X 2,201,721 5/1940 Elder 313337 X JOHN W. HUCKERT, Primary Examiner.

A. J. JAM-ES, Assistant Examiner. 

